You have an Azure AD tenant contoso.com and VNET1. An Azure AD DS managed domain litwareinc.com is deployed to VNET1. You plan to deploy an Azure Virtual Desktop host pool Pool1 to VNET1 and need to deploy Windows 10 Enterprise session hosts. What should you do first?

To deploy Azure Virtual Desktop session hosts that can join an Azure AD DS managed domain, the virtual network (VNET1) must be configured to use the Azure AD DS domain controllers for DNS resolution. By modifying the DNS settings of VNET1 to point to the IP addresses of the Azure AD DS domain controllers, the session hosts will be able to locate and join the litwareinc.com domain. Modifying the settings of the litwareinc.com DNS zone is incorrect because the managed domain's DNS is already configured by Azure AD DS; you need to direct the VNet to use it. Adding a custom domain name to contoso.com is irrelevant for joining session hosts to an Azure AD DS managed domain. Implementing Azure AD Connect cloud sync is for synchronizing identities between on-premises AD and Azure AD, not for VNet DNS configuration for Azure AD DS.